At the time, the carnage of the end-Permian overshadowed another extinction event just eight million years earlier at the end of the Guadalupian epoch. Over the last three decades, though, geologists have been digging deeper into the end-Guadalupian, and it’s more widely recognized as a distinct crisis. Now, some scientists are arguing that this ancient die-off was big enough to rank among the pantheon of past apocalypses, and they propose renaming the group of major extinction events the Big Six.
One factor that to be consistent with these mass extinction events, whether they were caused by extra-planetary asteroids or planetary volcanism is oxygen-depletion of the oceans. A condition that they have in common with our current anthropomorphic greenhouse warming.
In the past decade ocean oxygen levels have taken a dive—an alarming trend that is linked to climate change, says Andreas Oschlies, an oceanographer at the Helmholtz Center for Ocean Research Kiel in Germany, whose team tracks ocean oxygen levels worldwide. “We were surprised by the intensity of the changes we saw, how rapidly oxygen is going down in the ocean and how large the effects on marine ecosystems are,” he says.
The evidence becomes more compelling every day. The very processes that sustain life on our planet are under attack and this time it is not some random rock from space or fire from below the planet's surface that are besieging the planet. It is us - the most "intelligent" creature on the planet - we are the agents of another mass extinction event.
In the history of life, there have been many flameouts and setbacks. But by singling out and studying the biggest ones, geologists can begin to unearth patterns and search for common causes. Increasing evidence suggests that many global extinction events were associated with oxygen-depletion in the oceans, a symptom of greenhouse warming, and that has worrying implications for the present-day effects of climate change...
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